The Elements of Electricity
Voltage Current Resistance Types of Current: AC and DC Circuits
Closed Open Short

and Resistance
Water flowing through a hose is a good way to imagine electricity
Water is like Electrons in a wire (flowing electrons are called Current) Pressure is the force pushing water through a hose Voltage is the force pushing electrons through a wire Friction against the holes walls slows the flow of water Resistance is an impediment that slows the flow of electrons
. Current.Voltage.

Forms of Current
There are 2 types of current
The form is determined by the directions the current flows through a conductor
Direct Current (DC)
Flows in only one direction from negative toward positive pole of source
Alternating Current (AC)
Flows back and forth because the poles of the source alternate between positive and negative
.

AC Current Vocabulary
Time Period of One Cycle
.

Circuits
A circuit is a path for current to flow Three basic kinds of circuits
Open the path is broken and interrupts current flow Closed the path is complete and current flows were it is intended Short an unintended low resistance path that divers current
.

you made a mistake!
. If you blow a fuse. watch what you touch! The probes have sharp points so that you can make precise contacts. Be cautious. be attentive. Observe the meter maximum limits for voltage and current. the voltage being measured is exposed to the operator and flowing through the probes.Safety
When measuring voltage.Measuring Voltage . Fuses are a last resort protection feature. Use the protective shields when probes not in use.

the meter probes are placed across the voltage source. measuring AC voltages is not a simple matter. Because AC is a constantly changing wave form. This VOM measures pseudo-Root Mean Square (RMS) voltages
.Measuring voltage
Voltage type DC and AC
When measuring voltage. The VOM uses two separate functions and ranges to measure DC and AC.

more expensive meters will measure both currents. To measure current. the VOM must be inserted into the circuit so that the current
. there are two kinds of current associated with the voltage.Measuring Current
There is a greater potential for meter damage when measuring current than with any other function. Just as in voltage. This meter will only measure DC current. AC and DC.

high up to 10 amps. a hardy fuse to handle up to 10 amps of current and a more fragile fuse to protect the sensitive circuits needed to measure small currents.
Because there is such a wide range between the current scales. there are two physical probe jacks for the two ranges This allows for better protection. and low 200 milliamps (. Internal fuses provide some meter protection for over current situations.2 amps) and below.Measuring Current
There are two current ranges. Don t count on the fuses to protect the meter!
.

Measuring Current
CAUTION!!!!!!! There must be some resistance in the circuit or the current flow through the circuit will be the maximum the source will produce. DO NOT CONNECT THE VOM PROBES DIRECTLY ACROSS THE BATTERY POLES IN THE CURRENT MEASURMENT
. AND THIS CURRENT LEVEL COULD DAMAGE THE VOM! In other words.

so be patient.Measuring Current
We will be demonstrating some concepts during the current measurement exercises that will be covered in more detail later.
. In the following exercises you will use various resistors to limit the current flow in a simple circuit. it will all come together in the end.

The Proto Board
.

Measuring Current Basic Circuit
VOM Battery +
.

practice touching the VOM probes to the exposed wire ends. (m here is short for mA) Without connecting the battery. brown). Connect a wire to the + power source. Set VOM current scale to 200 m.
. black. connect another wire to the top end of the resistor (the non grounded end).First Current Measurement
Set up the circuit using a 100 ohm resistor (brown.

touch the black lead to the wire hooked to the top side of the resistor. Note the VOM reading. With the VOM set to the 200 m current scale.
.First Current Measurement
Connect the battery. Touch the red lead to the lead coming from the + side of the battery.

First Current Measurement
Now reverse the VOM leads and note the reading.
.

Change the VOM current ranges down and note the display readings What is the best range for measuring the current from a 9 volt source through a
200 m Range
100 ohm resistor?
20 m Range
.First Current Measurement
Return the VOM leads so that the red is connected to the battery.

red). black.
. Measure current using the 200 m range.Measuring Current
Wire the circuit with a 1k ohm resistor (brown.

Measuring Current
What is the best range to measure the current through a 1 k-ohm resistor?
200 m
20 m
2000 u
.

. orange).Measuring Current
Wire the circuit with a 10 k-ohm resistor (brown. black. Measure current with the 2000 u range.

Measuring Current
What is the best range to use to measure the current through a 10 k-ohm resistor at 9 volts?
2000 u
200 u
.

What is the best range to use to measure the current trough a 100 kohm resistor at 9-volts?
.Measuring Current
Wire the circuit with a 100 k-ohm resistor (brown. yellow). Begin with the 2000 m range. black. and measure the current at each range.

Remember k means multiply the reading by 1000.Measuring Resistance
When the VOM is used to measure resistance. An out of resistance reading will be indicated by a single 1 digit. what actually is measured is a small current applied to the component.
. Operating voltages should be removed from the component under test or you could damage the VOM at worst. There are 5 ranges. or the reading could be in error at best.

Select the 200 ohm range and touch the probe leads to both sides of the resistor.Measuring Resistance
Disconnect the battery from the board. no additional wires are required. Put the 100 ohm resistor in place.
. remember to measure resistance with the circuit un-powered.

Any difference?
.Measuring Resistance
Now reverse the probe leads and observe the reading.

measure the resistance using each of 20 k-ohm the other ranges.
. Note that the resolution of the reading decreases as the 200 k-ohm maximum ohm reading increases.Measuring Resistance 2000 ohm
Now using the 100 ohm resistor. down to the point where it is difficult to get a useful 2000 k-ohm resistance reading.

Measuring Resistance
Now use the 1k ohm resistor and the 200 range.
200
2000
. Explain the reading you observe.000 ohms (1 k-ohm). Find the appropriate range to measure 1.

predict the reading and confirm your prediction by taking the measurements
. using higher ranges.Measuring Resistance
Now use the 10 k-ohm and the 100 kohm resistor. First determine the appropriate range to use for each resistor. Second make the resistance measurements Third.

Measuring Resistance
Just for fun.
The voltage and current used by the VOM is not dangerous.
. use the VOM to measure the resistance offered between different body parts.
Discuss your observations and how your measurement techniques could influence the readings you get from the VOM.

there is heat generated All materials exhibit some resistance. even the best of conductors
Unit measured in Ohm(s)
From 1/10 of Ohms to millions of Ohms
.Resistance Defined
Resistance is the impediment to the flow of electrons through a conductor
(friction to moving electrons) Where there s friction.

Turn resistor so gold. silver band. The next band to the right is the second value digit 5.Reading Resistor Color Codes
1. Note the color of the third band from the left. or space is at right 2. this is the multiplier 6. Note the color of the two left hand color bands 3. Multiply the 2 value digits by the multiplier
. The left most band is the left hand value digit 4.

5.
. Physical size (the surface area available to dissipate heat) is a good indicator of how much heat (power) a resistor can handle Measured in watts Common values ¼. ½. 10 etc. 1.Power dissipation
Resistance generates heat and the component must be able to dissipate this heat to prevent damage.

. the components are in series. if there is only one path.Resistors in Circuits Series
Looking at the current path.

Resistors in Circuits Series
RE ! R1 R2 Rn
.

R1
R2
.Resistors in Circuits Series
On your proto board set up the following circuit using the resistance values indicated on the next slide. Calculate the equivalent resistant RE and measure the resistance with your VOM.

the circuit is a parallel circuit.
.Resistors in Circuits Parallel
If there is more than one way for the current to complete its path.

Resistors in Circuits Parallel
!
1
2 2
1
!
1
1
1 1
2
1
n
.

Calculate the equivalent resistant RE and measure the resistance with your VOM
R1
R2
.Resistors in Circuits Parallel
On your proto board set up the following circuit using the resistance values indicated on the next slide.

Resistors in Circuits Mixed
If the path for the current in a portion of the circuit is a single path, and in another portion of the circuit has multiple routes, the circuit is a mix of series and parallel.
Series Parallel

Take the parallel segment of the circuit and calculate the equivalent resistance:

R2 R3 RE ! R2 R3

R2 4.7K

R3 2.2K

The parallel resistors have been replaced by a single resistor with a value of 1498 ohms.Resistors in Circuits Mixed
R1 330 We now can look at the simplified circuit as shown here. Calculate the resistance of this series circuit:
RE=1498
R1 RE
.

solve each section and then combine them all back into the whole.2K R4 = 4. R1 = 330 R2 = 1K R3 = 2.Resistors in Circuits Mixed
In this problem.7K
R1
Series
Series
R2 R4 R3
r llel
. divide the problem into sections.

Ohm¶s Law
The mathematical relationship
E=I*R
Doing the math Kirchhoff s law
A way to predict circuit behavior It all adds up Nothing is lost
.

That relationship is Ohm s law.
E = volts R = resistance in ohms I = current in amps
E ! I *R
E R! I
E I! R
.Ohm¶s Law
There is a mathematical relationship between the three elements of electricity.

Ohm¶s Law
.

resistance and current. The VOM will be moved to measure voltage.Ohm¶s Law
This is the basic circuit that you will use for the following exercises.
A
V
.

Ohm¶s Law Exercise 1
Wire this circuit using a 100 ohm resistor. Without power applied measure the resistance of the resistor. Record your data. Connect the 9 volt battery and measure the voltage across the resistor.
V
.

How does the measured current compare to your prediction using Ohm s law?
A
. Using the appropriate current range. measure the actual current in the circuit.Ohm¶s Law Exercise 1
Insert the VOM into the circuit as indicated in this diagram.

A
.Ohm¶s Law Exercise 2
Select the 1K ohm resistor and create the illustrated circuit. Record your data. Measure the resistance with power removed and then the current with power applied. Pretend for this exercise that you do not know what the voltage of the battery is.

The example data results in a voltage of 9.73 volts
E ! I *R
.Ohm¶s Law Exercise 2
Using the current and resistance data taken in the last step use Ohm s law to calculate the anticipated voltage.

Ohm¶s Law Exercise 2
Connect the VOM into the circuit as indicated in this diagram. How does the voltage compare to your prediction using Ohm s law?
V
. Using the appropriate voltage range. measure the actual voltage across the resistor.

Ohm¶s Law Exercise 3
In this exercise you will use an unknown resistor supplied by your instructor. Create the circuit illustrated and measure the voltage and current. Record your data.
A

V

Ohm¶s Law Exercise 3
Using Ohm s law with the voltage and current, calculate the value of resistance. The example data results in a resistance of 3844 ohms.

E R! I

Ohm¶s Law In Practice
The next series of exercises will put Ohm s Law to use to illustrate some principles of basic electronics. As in the previous exercise you will build the circuits and insert the VOM into the circuit in the appropriate way to make current and voltage measurements. Throughout the exercise record your data so that you can compare it to calculations.

Ohm¶s Law In Practice
Now move the VOM to the other side of the circuit and measure the current. The current should be the same as the previous measurement.
+
A
-
.

There should be no surprise that the current is the same.
+
A
-
.Ohm¶s Law In Practice
Insert the VOM at the indicated location and measure the current.

.Ohm¶s Law In Practice
V
Measure the voltage across R1. calculate the voltage drop across a 1K ohm resistor at the current you measured Compare the result. Using Ohm s law.

Add the currents and compare and contrast to the current measured entering the total circuit. Record your current readings for both places. #1
A A
#2
.Ohm¶s Law In Practice
In this next step. you will insert the VOM in the circuit at two places illustrated at the right as #1 and #2.

calculate the voltage drop across the resistor.Ohm¶s Law In Practice
Using the current measured through #1 and the resistance value of R2. 2. Compare and contrast these two voltage values
. Likewise do the same with the current measured through #2 and the resistance value of R3. 1k ohms.2k ohms.

V
. Compare and contrast the voltage measured to the voltage drop calculated.Ohm¶s Law In Practice
Measure the voltage across the parallel resistors and record your answer.

Ohm¶s Law In Practice
In the next step. insert the VOM into the circuit as illustrated. Compare and contrast the current measured to the total current measured in a previous step. Were there any surprises?
A
. measure and record the current.

Insert the VOM into the circuit as illustrated and measure the voltage.Ohm¶s Law In Practice
Using the current you just measured and the resistance of R4 (330 ohms). Compare and contrast the measured and calculated voltages. calculate what the voltage drop across R4 should be.
V
.

Ohm¶s Law In Practice
There is one final measurement to complete this portion of the exercise. Insert the VOM as indicated. Recall the 3 voltages measured previously; across R1, R2 and R3, and across R4. Add these three voltages together and then compare and contrast the result with the total voltage just measured.

V

Ohm¶s Law In Practice
What you observed was:
The sum of the individual currents entering a node was equal to the total current leaving a node . The sum of the voltage drops was equal to the total voltage across the circuit.

This is Kirchhoff s law and is very useful in the study of electronic circuits. You also noted that Ohm s law applied throughout the circuit.

Two conductive plates separated by a non conductive material.
. temporary storage battery. Electrons accumulate on one plate forcing electrons away from the other plate leaving a net positive charge.The Capacitor Defined
A device that stores energy in electric field. Think of a capacitor as very small.

Insulating material between plates.The Capacitor Physical Construction
Capacitors are rated by:
Amount of charge that can be held.
. The voltage handling capabilities.

Notice the component has polarity identification + or -.Charging a Capacitor
In the following activity you will charge a capacitor by connecting a power source (9 volt battery) to a capacitor. You will be using an electrolytic capacitor. a capacitor that uses polarity sensitive insulating material between the conductive plates to increase charge capability in a small physical package.
+
.

Using your VOM. This short circuits the capacitor to make sure there is no residual charge left in the capacitor.Charging a Capacitor
Touch the two leads of the capacitor together. measure the voltage across the leads of the capacitor
.

Carefully observe the voltage reading over time until the voltage is at a very low level (down to zero volts). Quickly remove the capacitor from the circuit and touch the VOM probes to the capacitor leads to measure the voltage.
+
. Power will only have to be applied for a moment to fully charge the capacitor.Charging a Capacitor
Wire up the illustrated circuit and charge the capacitor.

Discharging a Capacitor
.

The capacitor essentially blocks DC current from passing through.The Capacitor Behavior in DC When connected to a DC source.
. the capacitor charges and holds the charge as long as the DC voltage is applied.

During the next half of the cycle.The Capacitor Behavior in AC
When AC voltage is applied. the capacitor is discharged then recharged in the reverse direction. during one half of the cycle the capacitor accepts a charge in one direction. It acts as if AC current passes through a capacitor
. During the next half cycle the pattern reverses.

The Capacitor Behavior A capacitor blocks the passage of DC current A capacitor passes AC current
.

The Capacitor Capacitance Value
The unit of capacitance is the farad. Most electronic devices use capacitors that are a very tiny fraction of a farad.
A single farad is a huge amount of capacitance.
Common capacitance ranges are:
Micro Nano Pico
Q
10-6 10-9 10-12
n
p
.

The Capacitor Capacitance Value
Capacitor identification depends on the capacitor type. or numbers. dots.
. Could be color bands. Wise to keep capacitors organized and identified to prevent a lot of work trying to re-identify the values.

Moving or changing magnetic fields cause electrons to move. 2.
. Moving electrons create a magnetic field.
An inductor is a coil of wire through which electrons move. and energy is stored in the resulting magnetic field.The Inductor
There are two fundamental principles of electromagnetics:
1.

The Inductor
Like capacitors. When the source of electrons is removed.
. the magnetic field collapses immediately. Unlike capacitors:
Inductors store energy in a magnetic field. not an electric field. inductors temporarily store energy.

Can be air wound (just air in the middle of the coil) Can be wound around a permeable material (material that concentrates magnetic fields) Can be wound around a circular form (toroid)
.The Inductor
Inductors are simply coils of wire.

Typical inductor values used in electronics are in the range of millihenry (1/1000 Henry) and microhenry (1/1.000. A Henry is a measure of the intensity of the magnetic field that is produced.The Inductor
Inductance is measured in Henry(s).000 Henry)
.

Diameter of coil. Spacing between turns. Type of material inside the coil.The Inductor
The amount of inductance is influenced by a number of factors:
Number of coil turns.
. Size of the wire used.

Inductor Performance With DC Currents
When a DC current is applied to an inductor, the increasing magnetic field opposes the current flow and the current flow is at a minimum. Finally, the magnetic field is at its maximum and the current flows to maintain the field. As soon as the current source is removed, the magnetic field begins to collapse and creates a rush of current in the other direction, sometimes at very high voltage.

Inductor Performance With AC Currents
When AC current is applied to an inductor, during the first half of the cycle, the magnetic field builds as if it were a DC current. During the next half of the cycle, the current is reversed and the magnetic field first has to decrease the reverse polarity in step with the changing current. These forces can work against each other resulting in a lower current flow.

The Inductor
Because the magnetic field surrounding an inductor can cut across another inductor in close proximity, the changing magnetic field in one can cause current to flow in the other the basis of transformers

The Diode
The semi-conductor phenomena Diode performance with AC and DC currents Diode types
General purpose LED Zenier
.

The Diode The semi-conductor phenomena
Atoms in a metal allow a sea of electrons that are relatively free to move about. Semiconducting materials like Silicon and Germanium have fewer free electrons. Impurities added to semiconductor material can either add free electrons or create an absence of free electrons (holes).
.

.The Diode The semi-conductor phenomena
Consider the bar of silicon at the right. The anode In between is a no man s land called the P-N Junction. The other side is doped with positive material (excess holes). The cathode.
One side of the bar is doped with negative material (excess electrons).

The Diode The semi-conductor phenomena
Consider now applying a negative voltage to the anode and positive voltage to the cathode.
. This diode is reverse biased meaning no current will flow. The electrons are attracted away from the junction.

The Diode The semi-conductor phenomena
Consider now applying a positive voltage to the anode and a negative voltage to the cathode. The electrons are forced to the junction. This diode is forward biased meaning current will flow.
.

The Diode
Set up the illustrated circuit on the proto board.
A
330
. The 330 ohm resistor in the circuit is a current limiting resistor (to avoid excessive diode current). Note the cathode (banded end) of the diode.

The Diode
Use the same circuit.
A
. Measure and record the current. but reverse the diode.

the diode is reversed biased and current stops. During the other half of the cycle.
. allowing current to flow in only one direction.
This is the process of rectification.The Diode with AC Current
If AC is applied to a diode:
During one half of the cycle the diode is forward biased and current flows. This is used to convert AC into pulsating DC.

this forms an LED. photons of light are emitted.
. when electrons combine with holes current flows and heat is produced.The Light Emitting Diode
In normal diodes. With some materials. when electrons combine with holes. LEDs are generally used as indicators though they have the same properties as a regular diode.

330
.The Light Emitting Diode
Build the illustrated circuit on the proto board. Observe the diode response Reverse the LED and observe what happens. The current limiting resistor not only limits the current but also controls LED brightness. The longer LED lead is the anode (positive end).

Zener Diode
A Zener diode is designed through appropriate doping so that it conducts at a predetermined reverse voltage.
The diode begins to conduct and then maintains that predetermined voltage
9V
4.7V
The over-voltage and associated current must be dissipated by the diode as heat
.

NPN
. not pointing in.The Transistor
There are two basic types of transistors depending of the arrangement of the material.
The only operational difference is the source polarity.
PNP NPN
PNP
An easy phrase to help remember the appropriate symbol is to look at the arrow.
PNP NPN pointing in proudly.

The pin out of the 2N3904 transistor is indicated here.
E
B C
.The Transistor Switch
During the next two activities you will build a transistor switch and a transistor amplifier.

Use hook up wire to serve as switches to connect the current to the transistor base. What happens when you first apply power when the base is left floating (not connected)?
330
9-volt
1000
.The Transistor Switch
Build the circuit on the proto board.

Touch the other end (supply 9 volts) to the resistor in the base line and observe what happens.The Transistor Switch
Make the illustrated adjustment to the circuit. Connect one end of some hook-up wire to the positive side of the 9 volt battery.
330
1000
.

V
1000
.5 volt battery as shown.The Transistor Switch
Now replace the hookup wire connection with a connection to a 1.5 volts is applied to the base? What happens when the battery is reversed and 1. What happens when +1.5 volts is applied to the base?
330 9V
1.

The Transistor Switch
When does the transistor start to turn on? Build up the illustrated circuit with the variable resistor in the base circuit to find out.
330 9V
1000
.

Putting It All Together
Simple construction project
.

Conclusion
Not really . This course was intended to introduce you to some concepts and help you become knowledgeable in others.your journey to understand basic electronics has just begun.
.